Subtropical Areas Warming Faster; Jet Streams Moving Poleward

30 May 2006

Satellite data shows more rapid warming in the sub-tropical region of the troposphere, and concomitant cooling in the stratosphere.

By examining more than 25 years of satellite data, a team of researchers has found that the atmosphere is warming faster in subtropical areas, around 30 degrees north and south latitude, than it is elsewhere. They also found that each hemisphere’s jet stream has moved toward each pole by about 1 degree of latitude, or 70 miles.

The evidence, published in the 26 May edition of Science, matches global warming computer models; the result could be a widening of the tropics and an expansion of some of the world’s driest regions.

It is direct observational evidence of atmospheric circulation changes seen from satellites.

—Qiang Fu, University of Washington and lead author

The researchers note that it is not clear yet whether the movement of the jet streams is key evidence for global warming or just an anomaly, and that more work is needed to understand precisely why the jet streams are moving. If the movement continues, the long-term impact on rainfall could be serious.

The jet streams mark the edge of the tropics, so if they are moving poleward that means the tropics are getting wider. If they move another 2 to 3 degrees poleward in this century, very dry areas such as the Sahara Desert could nudge farther toward the pole, perhaps by a few hundred miles.

—John M. Wallace, University of Washington

The researchers analyzed satellite temperature data collected from 1979 through 2005 and found the troposphere was warming faster in a band around 30 degrees north latitude—which crosses the southern United States, southern China and north Africa—and around 30 degrees south latitude -- which crosses southern Australia, South Africa and southern South America. The troposphere is the layer from the Earth’s surface to about 7.5 miles in altitude, the part of the atmosphere in which most weather occurs.

While a poleward shift of jet streams is a strongly supported prediction by computer models of 21st century climate, the models also show the fastest warming will occur in the tropical upper troposphere. Instead, the research found that warming was actually a bit faster at 30 degrees latitude in both hemispheres than over the equator.

The enhanced warming at 30 degrees latitude has helped to reshape the atmosphere’s pressure surfaces in a way that pushed the jet streams toward the poles. The position of the jet streams—the band of strongest westerly winds aloft—is important because it determines the northern and southern limits of the major wet and dry belts on the surface.

The scientists examined measurements from microwave-sounding units on NOAA satellites. The satellites use similar equipment and techniques to measure microwave radiation emitted by oxygen in the atmosphere and determine its temperature.

Fu and colleagues previously analyzed these measurements to show that the troposphere actually is warming as much as the Earth’s surface, a key piece of evidence to demonstrate that the Earth is warming faster than can be accounted for by natural processes.

The new research suggests that faster subtropical warming of the troposphere, which moves the jet streams, also could shift mid-latitude storm tracks poleward, Wallace said. That could reduce winter precipitation in regions such as southern Europe, including the Alps, and southern Australia.

Fu noted the research also appears to show that enhanced warming in the troposphere corresponds closely with enhanced cooling in the stratosphere, which extends from about 7.5 miles in altitude to about 31 miles.

It’s a very intriguing problem, why the increase in tropospheric temperatures and the decrease in stratospheric temperatures in the subtropical region happens in tandem, almost exactly.

—Qiang Fu

The work was supported by grants from the National Oceanic and Atmospheric Administration and the National Aeronautics and Space Administration.

Comments

I notice in these articles they always focus on the bad consquences. Apparently nothing good can ever come of climate change.

It's particularly bizarre to read this juxtaposition: widening of the tropics, and expansion of the driest areas. Let's see. What's the kind of climate you think of when you hear the word "tropical"? Dry, harsh desert? Wrong. You think of moist, humid, air, luxuriant growth, the highest biomass content per square meter of any region on earth.

Either this connection is wrong, or expanding the tropics might actually increase precipitation in some areas. Why didn't the article mention that? Why was it all about expanding the Sahara? Probably, because increasing the range of tropical moisture would not sound as harmful.

I accept the scientific consensus on this issue, that global warming is happening and that it is influenced at least in part by human activity. But these kinds of articles, that always accentuate the harmful consequences, make me question the objectivity of the scientific community on this issue. Science should be about giving us the facts, good and bad; then, society decides what to do about them.

I have never read a mainstream or scientific article about climate change which mentioned good consequences without also mentioning bad ones; but I have many times read articles that mention bad consequences without listing any good ones. See if you find this to be true in your reading about the issue. IMO it is clear evidence that the issue is being presented in a one sided manner.

Excellent points, Hal! I picture the Earth as a self-healing organism. It wants to correct itself to an optimal temperature range. As the temperature increases so does the moisture level which inherently blocks the sun more and causes a cooling effect. I would predict with this present jet stream pattern that the lower United States would see more precipitation and hurricane activity would extend up to the northern regions (perhaps once again hitting New York). Costal flooding inland for 100-200 miles as the polar caps melt and the added benefit of beachfront property in the tropical region of Arizona.

I agree there may be some winners with global warming (wheat farmers in Canada?), but the scientific consensus is that it's mostly a lose-lose proposition for most of the species on the planet. The biosphere that supports us evolved under a cooler climate regime than the one we're headed for. A new and different biosphere may evolve under the new regime, but I personally won't be around to see it, nor will my great-great-grandchildren, if any. In the meantime, the stress of the changeover is likely to have tragic consequences for many species, including ours.

It's particularly bizarre to read this juxtaposition: widening of the tropics, and expansion of the driest areas. Let's see. What's the kind of climate you think of when you hear the word "tropical"? Dry, harsh desert? Wrong. You think of moist, humid, air, luxuriant growth, the highest biomass content per square meter of any region on earth.

Actually the regions of concern are the subtropics -- these regions are quite dry (look on a world map and note that the Sahara, SE US and N Mexico, much of the Middle East in the North; the Chaco and Great Australian Deserts in the South are all at about the same latitude.) The spread of arid regions is, however, in large part driven by increased convection in the tropics proper.

I have never read a mainstream or scientific article about climate change which mentioned good consequences without also mentioning bad ones

Well, the general consensus is that the bad consequences outnumber the good. Change is hard.

We must accept Warming, as one gets zits on the face, after eating good chocolate. All we can do is let nature take its course and eventually it will heal its self.
Man is too hooked on the good things that convenient energy gives us.
Market and political forces, will force coal and oil to be used until depleted.
It is impossible to stop burning this stuff!
So, relax, chill out, and hope there will be some "good" with the "bad" of Warming.

I think it is absolutely reprehensible for our current generations, who are making the decisions now, to be passing on such uncertainty to future generations. There are many examples of our forefathers showing much more foresight than this.

The really stupid thing is that everybody assumes that reducing CO2 emissions has to mean damaging our economies. This garbage is fed by narrow minded economic fundamentalists and too many people are swallowing it.

The economony of some countries (including USA and Canada) benefited significantly from Oil give-a-way (or help yourself for as little as $3/barrel) for almost 100 years. Cheap oil/gas inspired the construction and use of rediculous inefficient Hummer style and heavy 4 x 4 pick-ups and other gas guzzlers with their associated high GHG emission and climate change effects.

Luckily, cheap fossil liquid fuel will run out soon and the price will keep going up and/or it will be taxed sufficiantly to raise the price above $5/gal or high enough to discourage the use of current gas guzzlers and inefficient ICE vehicles.

At $100+ per week (20 gal x $5) to fuel the family car or light truck, we will find the extra $5K to $10K for a 100 mpg PHEV very acceptable and transition could be accellerated.

Even current Toyota Prius II/III and other similar hybrids with their 40 to 60 mpg efficiency can reduce fuel consumption by a factor of 2 to 3, reducing the weekly gas bill from $100 to $33 - $50. Hybrids would sell well with higher gas prices but produce too much GHG (3 to 4 ton per car/year). PHEVs and eventually EVs are better solutions.

Man-made CO2 induced climate changes (on top of the current natural cycle) will benefit very few of us (mostly in Canada and extrem northern USA) but could jeopardize the living style of the majority living near the oceans and in mid and southern USA. Any thing above the natural long term upward natural cycle should not be regarded as being positive.

Hal, the greatest population centers of the world are in the tropic and subtropical area, such as India, 1/2 of China, South and Central America and Mexico, Middle East etc... We are having enough trouble controlling our southern border, being flooded with 12 millions illegal aliens. Border towns are rifed with deadly crimes and murders. Imagine the ten-fold increasing in invasion of illegal immigration due to their land become invaded by rising coastline or uninhabitable by drought. There will be more wars and conflicts. There will be more mosquitoes, malaria (already a number one killer world-wide with highly resistant protozoans), and other tropical diseases. Tropical diseases are very nasty, and yet, luckily, we have not heard of it much here in the temperate zones, but just wait and see. Those in the temperate zones not having natural immunity to those diseases will perish like the American Indians from European's small pox.
In short, there will be hell on earth with uncontrolled global warming, even for those living in colder northern areas.